Multi-Stage Burner Fuel Ejection for Low-NOx Flame Stability
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Solution Overview
Problem
Existing burner designs struggle to significantly reduce NOx emissions while maintaining flame stability and turndown ratios, particularly in industrial combustion systems like heaters and boilers, due to high flame temperatures that break N2 bonds and form thermal NOx.
Innovation Solution
The burner apparatus employs a multi-stage fuel ejection system with primary, secondary, and tertiary fuel streams that entrain flue gas through radial impact structures, enhancing internal flue gas recirculation (IFGR) to lower peak flame temperatures and stabilize combustion, achieving reduced NOx emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the flame temperature is increased to improve combustion efficiency, then the combustion rate increases, but thermal NOx emissions increase due to broken N2 bonds
Solution Approach 1:
The fuel combustion process is divided into multiple stages with different air-to-fuel ratios. The first stage uses a rich mixture (excess air ratio 0.6-0.8) to limit peak temperature and reduce NOx formation, while subsequent stages introduce additional air to complete combustion. This segmentation allows the combustion rate to be maintained through staged burning while preventing thermal NOx formation by keeping peak temperatures below the N2 bond breaking threshold.
Solution Approach 2:
Combustion air is preheated to a temperature between 200°C and 400°C before entering the combustion zone. This preliminary heating of the air improves combustion efficiency and maintains a high combustion rate, while the controlled preheat temperature prevents excessive peak flame temperatures that would break N2 bonds and form thermal NOx.
2Object-generated harmful factors
If flue gas recirculation is increased to reduce peak flame temperature and NOx emissions, then thermal NOx formation decreases, but flame stability deteriorates
Solution Approach 1:
The flue gas recirculation is implemented in a staged manner, with the first combustion stage using a rich mixture that naturally limits peak temperature, and subsequent stages introducing air to complete combustion. This segmented approach reduces the need for excessive flue gas recirculation while maintaining flame stability through controlled combustion progression.
Solution Approach 2:
The excess air ratio in the first combustion stage is optimized to 0.6-0.8, and the preheat temperature is maintained between 200°C and 400°C. These parameter changes allow the system to achieve low NOx emissions without requiring excessive flue gas recirculation that would compromise flame stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The burner achieves NOx emissions of 12 ppmv to 5 ppmv or less with increased IFGR, maintaining flame stability and turndown ratios, suitable for various industrial combustion systems.
Implementation Method 1
a multi-stage fuel ejection system with primary, secondary, and tertiary fuel streams that entrain flue gas through radial impact structures
Implementation Method 2
enhancing internal flue gas recirculation (IFGR) to lower peak flame temperatures
Implementation Method 3
thermal NOx is the primary mechanism for NOx production. Thermal NOx is produced when the flame reaches a high enough temperature to break the covalent N2 bond so that the resulting 'free' nitrogen atoms bond with oxygen to form NOx
Data Source
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AI summary
A burner apparatus and method which provide an increased amount of internal flue recirculation for reducing NOx emissions by ejecting a series of surrounding, primary fuel streams and also ejecting on one or more subsequent series of surrounding fuel streams outside of the burner wall toward the burner combustion wherein each succeeding series of surrounding fuel streams must travel a greater distance to the combustion zone and each series of surrounding fuel streams must contact one or more radial impact structures provided on the exterior of the burner wall.